For years, I have been using only synthetic lubrication in my best doubles, with excellent results, because, over time, it leaves no varnish-like build up, no residue build up at all, unlike petroleum based lubrication. I use grease on hinge pin, and oil on internal workings, where needed, all synthetic. Best synthetics not only do that, but they provide better lubrication, less friction, and are much improved over petroleum based lubs, though they cost more. More cost is meaningless, after all, how much does one use in a double? If you have ever taken apart good old classic doubles, you have seen this residue build-up that I am talking about, and you know negative effects of it.